I was just at the online Apple store to buy an iTunes gift card for my mother (who hopefully will not be reading this blog) -- when you arrive from iTunes, it drops you on a page where you can choose from a variety of gift card designs. On this screen, it seems that there is a 1:1 relationship between colors and denominations -- for example, the $25 card only comes in red.

I picked my denomination, and was taken to a page where I could enter a personalized message. Below that, I was offered the opportunity to "change theme":

I wasn't much a fan of the red, so I clicked to choose the green, entered my personalized message, and clicked add to cart -- and only then did I find out that changing the theme also changed my order to a more expensive card. That's either extremely poor design, or extremely sketchy.